Automatic refill system for an air conditioning system

ABSTRACT

An automatic recharge system ( 22 ) is provided for a transcritical cooling system ( 10 ). The recharge system ( 22 ) includes a refrigerant container ( 30 ) capable of storing a refrigerant charge at a higher pressure that can be accommodated on the low pressure side of the cooling system ( 10 ), and a control valve ( 34 ) connected between an outlet ( 36 ) of the container ( 30 ) and the low pressure side of the cooling system ( 10 ) to automatically control the release of refrigerant form the refrigerant container ( 30 ) for circulation in the cooling system ( 10 ).

FIELD OF THE INVENTION

This invention relates to air conditioning systems, and in more particular applications, to transcritical air conditioning systems that utilize refrigerant, such as CO₂.

BACKGROUND OF THE INVENTION

In cooling systems such as vapor compression type air conditioning systems, refrigerant leakage can take place over time, thereby reducing system performance and increasing the chance of damage to the compressor. While refrigerant leakage can take place in any cooling system and cause a loss of performance, such leakage can be particularly troublesome in transcritical cooling systems that utilize a variable displacement compressor. In such systems, if the refrigerant charge amount falls below a certain level due to leakage, the system will not be able to function normally and will experience a suction pressure that is below the normal operating limit, too much superheat from the evaporator, and a reduced displacement in the variable displacement compressor. As a result, the system will have a very small cooling capacity. In this regard, in systems that utilize an accumulator, it is known to provide extra volume in the accumulator in order to accommodate more refrigerant than is required to operate the system satisfactorily so that, as refrigerant leaks form the system, the additional refrigerant that is contained in the accumulator is circulated in the system to make up the lost refrigerant. While such systems may work satisfactorily for their intended purpose, they tend to increase the system size and weight because of the required increase in the size of the accumulator to accommodate the extra refrigerant.

SUMMARY OF THE INVENTION

In accordance with one feature of the invention, a transcritical cooling system is provided and includes a compressor to provide pressurized refrigerant to the system; a gas cooler connected downstream from the compressor to receive pressurized refrigerant therefrom and to supply cooled, pressurized refrigerant to the system; an expansion device connected downstream from the gas cooler to receive cooled, pressurized refrigerant therefrom and to supply reduced pressure, two-phase refrigerant to the system; an evaporator connected downstream from the expansion device to receive reduced pressure, two-phase refrigerant therefrom and connected upstream from the compressor to supply heated, reduced pressure refrigerant thereto; and an automatic refrigerant recharge system connected to the cooling system downstream from the evaporator and upstream from the compressor to automatically supply additional refrigerant for circulation through the system. The refrigerant recharge system includes a refrigerant container for storing a charge of refrigerant at a pressure greater than a pressure of the refrigerant exiting the evaporator, and a control valve connected between the container and the remainder of the system to control the release of refrigerant from the refrigerant container for circulation in the cooling system.

In one feature, the cooling system further includes an accumulator connected downstream from the evaporator to receive heated refrigerant therefrom and upstream from the compressor to supply gas phase refrigerant thereto. The control valve is connected to the accumulator to supply refrigerant thereto from the refrigerant container. In a further feature, the refrigerant recharge system is carried by the accumulator.

As one feature, the cooling system further includes a low pressure conduit connected between the evaporator and the compressor to transfer refrigerant from the evaporator to the compressor, and the refrigerant container is provided as a cylindrical tube extending along an exterior of the low pressure conduit.

According to one feature, the control valve includes a bleed valve having a preselected bleed rate into the cooling system based on anticipated refrigerant leakage from the cooling system.

In accordance with one feature, the control valve includes a normally off valve that is responsive to a signal from the system to temporarily open and supply a discrete amount of refrigerant to the cooling system. As a further feature, the cooling system further includes a plurality of sensors to monitor system parameters, and a control connected to the sensors and the control valve to provide the signal to the control valve in response to information from the sensors.

As one feature, the compressor is a variable displacement compressor.

In accordance with one feature of the invention, a method is provided for automatically recharging a transcritical cooling system that has leaked refrigerant, wherein the cooling system includes a compressor, a gas cooler, an expansion device, an evaporator and an accumulator volume all connected in series in a refrigerant loop. The method including the steps of:

a) storing a refrigerant in a recharge volume that is hydraulically isolated from the accumulator volume and at a pressure that is greater than the refrigerant pressure in the accumulator volume, the recharge volume being part of the cooling system during normal operation of the cooling system; and

b) automatically releasing refrigerant from the recharge volume into the system to replace refrigerant that has leaked from the cooling system.

As one feature, step b) includes continuously bleeding refrigerant into the cooling system from the recharge volume during normal operation of the cooling system.

In one feature, the method further includes the step of automatically monitoring the cooling system to determine if refrigerant should be released from the recharge volume into the cooling system, and step b) further includes releasing the refrigerant into the cooling system in response to the step of automatically monitoring. As a further feature, the step of automatically monitoring includes monitoring a suction line pressure of the cooling system, monitoring an ambient temperature, and monitoring a displacement of the compressor.

According to one feature, the method further includes the step of periodically replacing the recharge volume after the refrigerant has been depleted therefrom.

In accordance with one feature of the invention, a method is provided for automatically recharging a transcritical cooling system that has leaked refrigerant. The cooling system comprising a compressor, a gas cooler, an expansion device, and an evaporator all connected in series in a refrigerant loop. The method comprising the steps of:

a) storing a refrigerant in a recharge volume at a pressure that is greater than the refrigerant pressure in a suction side of the refrigerant loop, the recharge volume being part of the cooling system during normal operation of the cooling system; and

b) automatically releasing refrigerant from the recharge volume into the system to replace refrigerant that has leaked from the system.

Other objects, features, and advantages of the invention will become apparent from a review of the entire specification, including the appended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of an automotive air conditioning system including an automatic recharge system embodying the present invention;

FIG. 2 is a diagrammatic representation similar to FIG. 1, but showing an alternate embodiment of the automatic refill system; and

FIG. 3 is a graph of ambient temperature versus pressure inside a refrigerant charge cylinder showing the plots for the different volumes required to accommodate a 120 gram extra charge of CO₂ refrigerant.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, a transcritical cooling system 10 is shown and includes a refrigerant flow path or loop 12; a variable displacement compressor 14 to deliver pressurized refrigerant (typically carbon dioxide (“CO₂”)) to the flow path 12; a gas cooler 16 connected to the compressor 14 to receive the pressurized refrigerant therefrom; an expansion device 18 connected in the refrigerant flow path 12 downstream from the gas cooler 16 to receive cooled, pressurized refrigerant therefrom and to supply reduced pressure, liquid phase refrigerant to the flow path 12, often in the form of a two-phase refrigerant flow that includes the liquid phase refrigerant; an evaporator 20 connected to the expansion device 18 to receive reduced pressure, liquid phase refrigerant therefrom and deliver heated refrigerant back to the system 10; and an automatic refill or recharge system 22 connected to the low pressure side of the refrigerant flow path 12 between the evaporator 20 and the compressor 14 to automatically deliver refrigerant to the system 10 during normal operation of the system 10 as required by the leakage of refrigerant from the system 10. While not absolutely required, it is highly preferred that the system 10 further include an accumulator 24 connected downstream from the evaporator 20 to receive heated refrigerant therefrom and upstream from the compressor 14 to deliver gas phase refrigerant thereto. The accumulator 24 encloses an accumulator volume 25 for storing refrigerant and for separating liquid phase and gas phase refrigerant so as to supply gas phase refrigerant to the compressor 14. Again, while not absolutely required, it is also highly preferred that the system 10 further include a suction line heat exchanger, shown at 26, to transfer heat from the refrigerant in the high pressure side of the refrigerant flow path 12 to the refrigerant in the low pressure side of the refrigerant flow path 12. In this regard, the suction line heat exchanger 26 can either be integrated into the accumulator 24 as shown, or can be a separate heat exchanger, as is known.

The automatic refill system 22 will preferably include a refrigerant container 30, preferably in the form of a cylindrical housing 32, and a control valve 34 connected between an outlet 36 of the container 30 and the low pressure side of the refrigerant flow path 12 to control the flow of refrigerant from the container 30 into the remainder of the system 10. The container 30 encloses a recharge volume 38 that stores a mass of refrigerant for recharging the system 10, and preferably stores an adequate mass of refrigerant to recharge the system 10 over a number of years of operation.

In one of the most simple embodiments of the recharge system 22, the control valve 34 is provided in the form of a bleed valve having a bleed rate that would be set to allow a certain number of grams of refrigerant per year to bleed into the system in order to automatically compensate for the anticipated system leakage. For example, in one embodiment of the system 10, it would be anticipated that a bleed rate through the valve 34 should be about 20 grams of CO₂ refrigerant per year in order to automatically compensate for system leakage.

In another embodiment of the recharge system 22, the control valve 34 is provided in the form of a normally off valve, such as a solenoid valve, that is responsive to a signal from the system 10 to temporarily open and supply a discrete amount of refrigerant to the system 10. In this regard, sensors 42, 44 and 46 are preferably provided to monitor the suction pressure, compressor displacement, and ambient temperature during operation of the system 10 and to provide a signal to a controller 48. If the suction pressure goes below a predetermined level P_(L) for a certain period of time t_(P) (for example, five minutes after the system 10 is turned on) at moderate to high ambient temperature conditions (for example, ambient temperatures above 30° C.) while the compressor 14 is in partial displacement, the controller 48 would command the control valve 34 to open for a very short period of time (for example, one half of a second) to thereby supply a discrete amount of refrigerant to the system 10 in order to complete one automatic charge. After this, the system 10 will continue monitoring for the time period t_(P) and if the suction pressure is still below P_(L), the system will repeat the process. Otherwise, the recharge system 22 will be in waiting mode where the system 22 monitors the parameters from the sensors 42, 44 and 46 in order to determine if another automatic charge is required. At low ambient temperature conditions, the system 22 would stay in the waiting mode with the valve 34 closed.

The recharge system 22 is integrated as part of the cooling system 10 so that it can function during normal operation of the cooling system 10. In this regard, the refrigerant container 30 and valve 34 of the recharge system 22 can be mounted on or carried by the accumulator 24. However, it should be appreciated that there are many possibilities for integrating the recharge system 22 into the cooling system 10. For example, with reference to FIG. 4, an alternate embodiment of the system 10 is shown wherein the container 30 is provided in the form of a cylindrical tube 50, preferably of a small diameter (such as for example as small as 20 mm in diameter), that extends along a low pressure conduit 52 connected between the evaporator 20 and the compressor 14. In this regard, while the container 30 and conduit 52 are shown upstream of the accumulator 24, they could also be provided downstream of the accumulator 24.

It should be appreciated that all of the above described components for the system 10, including the components of the recharge system 22, have been described generically because there are many suitable forms for each of the components of the system 10 and the particular configuration selected will be highly dependent upon the requirements for each particular application, as can be determined by one skilled in the art. It should also be appreciated that by providing the control valve 34, the recharge system 22 can automatically provide refrigerant to the cooling system 10 while the transcritical cooling system is operating to make up for refrigerant loss due to leakage without requiring any human intervention.

While not shown, a quick disconnect, or other suitable fluid connection can be provided, preferably between the container 30 and the valve 34, to allow for the container 30 to be manually replaced when it has been depleted of its refrigerant charge, preferably after a number of years of operation of the cooling system 10.

FIG. 3 is a plot showing the differences in charge storage capacity based on the ambient temperature surrounding the system 10 and the pressure capacity of the container for the refrigerant. The plot assumes a 120 gram charge of extra refrigerant that can be used to compensate for refrigerant leakage over a five year period. Each line in the plot represents a different storage volume available for the 120 gram charge of refrigerant. It can be seen from the chart that the greater the pressure capability of the refrigerant container, the smaller the required volume for the refrigerant charge. For example, if the refrigerant container has a pressure limit of 110 Bar at 80° C. (as may be somewhat typical for an accumulator), a volume of 460 cm² is required to accommodate the 120 gram charge of refrigerant, but if the pressure limit of the storage volume is increased to 200 bar, the volume of the refrigerant container can be reduced to 200 cm². Thus, by providing a separate container 30 for the charge of refrigerant, the system 22 can store the refrigerant at a higher pressure than can be accommodated on the low pressure side of the system 10 and, therefore, can store the required charge of refrigerant in a much smaller volume than would be allowed in the accumulator 24. This can allow for a smaller system size and weight in comparison to a cooling system that attempts to accommodate system leakage by providing extra volume in the accumulator 24. 

1. A transcritical cooling system comprising: a compressor to provide pressurized refrigerant to the system; a gas cooler connected downstream from the compressor to receive pressurized refrigerant therefrom and to supply cooled, pressurized refrigerant to the system; an expansion device connected downstream from the gas cooler to receive cooled, pressurized refrigerant therefrom and to supply reduced pressure, two-phase refrigerant to the system; an evaporator connected downstream from the expansion device to receive reduced pressure, two-phase refrigerant therefrom and connected upstream from the compressor to supply heated, reduced pressure refrigerant thereto; and an automatic refrigerant recharge system connected to the cooling system downstream from the evaporator and upstream from the compressor to automatically supply additional refrigerant for circulation through the system; the refrigerant recharge system comprising a refrigerant container for storing a charge of refrigerant at a pressure greater than a pressure of the refrigerant exiting the evaporator, and a control valve connected between the container and the remainder of the system to control the release of refrigerant from the refrigerant container for circulation in the cooling system.
 2. The system of claim 1 further comprising an accumulator connected downstream from the evaporator to receive heated refrigerant therefrom and upstream from the compressor to supply gas phase refrigerant thereto; and wherein the control valve is connected to the accumulator to supply refrigerant thereto from the refrigerant container.
 3. The system of claim 2 wherein the refrigerant recharge system is carried by the accumulator.
 4. The system of claim 1 further comprising a low pressure conduit connected between the evaporator and the compressor to transfer refrigerant from the evaporator to the compressor; and wherein the refrigerant container is a cylindrical tube extending along an exterior of the low pressure conduit.
 5. The system of claim 1 wherein the control valve comprises a bleed valve having a preselected bleed rate into the cooling system based on anticipated refrigerant leakage from the system.
 6. The system of claim 1 wherein the control valve comprises a normally off valve that is responsive to a signal from the cooling system to temporarily open and supply a discrete amount of refrigerant to the cooling system.
 7. The system of claim 6 further comprising a plurality of sensors to monitor system parameters, and a control connected to the sensors and the control valve to provide the signal to the control valve in response to information from the sensors.
 8. The system of claim 1 wherein the compressor is a variable displacement compressor.
 9. A method of automatically recharging a transcritical cooling system that has leaked refrigerant, the cooling system comprising a compressor, a gas cooler, an expansion device, an evaporator and an accumulator volume all connected in series in a refrigerant loop, the method comprising the steps of: a) storing a refrigerant in a recharge volume that is hydraulically isolated from the accumulator volume and at a pressure that is greater than the refrigerant pressure in the accumulator volume, the recharge volume being part of the cooling system during normal operation of the cooling system; and b) automatically releasing refrigerant from the recharge volume into the system to replace refrigerant that has leaked from the system.
 10. The method of claim 9 wherein step b) comprises continuously bleeding refrigerant into the cooling system from the recharge volume during normal operation of the cooling system.
 11. The method of claim 9 further comprising the step of automatically monitoring the cooling system to determine if refrigerant should be released from the recharge volume into the cooling system; and wherein step b) further comprises releasing the refrigerant into the cooling system in response to the step of automatically monitoring.
 12. The method of claim 9 wherein the step of monitoring comprises monitoring a suction line pressure of the cooling system, monitoring an ambient temperature, and monitoring a displacement of the compressor.
 13. The method of claim 9 further comprising the step of periodically replacing the recharge volume after the refrigerant has been depleted therefrom.
 14. A method of automatically recharging a transcritical cooling system that has leaked refrigerant, the cooling system comprising a compressor, a gas cooler, an expansion device, and an evaporator all connected in series in a refrigerant loop, the method comprising the steps of: a) storing a refrigerant in a recharge volume at a pressure that is greater than the refrigerant pressure in a suction side of the refrigerant loop, the recharge volume being part of the cooling system during normal operation of the cooling system; and b) automatically releasing refrigerant from the recharge volume into the system to replace refrigerant that has leaked from the system.
 15. The method of claim 14 wherein step b) comprises continuously bleeding refrigerant into the cooling system from the recharge volume during normal operation of the cooling system.
 16. The method of claim 14 further comprising the step of automatically monitoring the cooling system to determine if refrigerant should be released from the recharge volume into the system; and wherein step b) further comprises releasing the refrigerant into the cooling system in response to the step of automatically monitoring.
 17. The method of claim 14 wherein the step of monitoring comprises monitoring a suction line pressure of the cooling system, monitoring an ambient temperature, and monitoring a displacement of the compressor.
 18. The method of claim 14 further comprising the step of periodically replacing the recharge volume after the refrigerant has been depleted therefrom. 